A wide variety of products, particularly perishable food products are sealed in packages using thermoplastic films sealed by vacuum skin packaging, thermoforming or other processes. In vacuum skin packaging, a product is placed on a support of a film or of a tray of relatively rigid material and, by differential air pressure, a heated thermoplastic film above the product is molded down upon and around the product and against the support, the space between the upper film and the support having been evacuated. The heated film forms a tight skin around the product and is sealed to the support.
In the thermoforming process the thermoplastic film is sealed to the flange-like edges of the support using heated sealing bars or similar equipment.
Other packaging processes for which the packaging material employs the peelable seal layer of the present invention include packaging in vertical or horizontal form-fill machines, as used in cereal packages and the like.
A problem that is encountered in these types of packaging is that the heated thermoplastic film seals so strongly to the support that it is difficult to separate them from each other in order to open the package. An easy to open package of this type should be easily openable by manually pulling apart the two films, normally starting from a point like a corner of the package where the film has purposely not been sealed to the support. In this manner the use of scissors, a knife or other devices to open the package can be avoided.
A packaging material described in EP 0 192 131 B1, which addresses this problem consists of an upper and lower web of a thermoplastic material and a seal layer disposed there between and adhered to each of the opposite surfaces of the two webs, the adhesive seal strength of the seal layer to the first and second surfaces being greater than its internal cohesive strength. To break the seal of such packages, the upper and lower webs are peeled apart manually, during which time the seal layer separates due to internal cohesive failure, whereby portions of the seal layer are left on the first and second surfaces.
The seal layer in these types of packaging materials can be a blend of an ionomer and a modified ethylene-vinyl acetate copolymer. While these materials work well, they have the disadvantage that ionomers tend to be relatively costly in comparison to other thermoplastics, therefore commercially unattractive for certain end-uses.
Accordingly, it is an object of the present invention to provide a lower cost alternative polymer blend for use as a peelable seal layer in packaging. More particularly, it is an object of the present invention to provide a peelable seal layer formed from a thermoplastic polymer blend comprising (a) a non-polar polyolefin and (b) a polar ethylene copolymer having carbon monoxide functionality; whereby component (b) is present in the blend in a weight range between 1 and 90%; and to provide a packaging material comprising the peelable seal layer and a thermoplastic film.